Variable gap reluctance transducer



Jan. 5, 1960 A. A. c-ERNosKY 2,920,307

VARIABLE GAP RELUCTANCE TRANsDUcER Filed Juy 19, 1954 s sheets-sheet 2 INVENTOR. A//en A. Chemas/ry, BY

AGENT.

Jan- 5, 1960 A. A. cHERNosKY 2,920,307

VARIABLE GAP RELUCTANCE TRANsDucER Filed July 19, 1954 3 Sheets-Sheet 3 GRAPH/CAL SOLUT/ON ALN/CO Y /NUC TIOIV KILOGA USS DEMAa/VEr/ZA r/av Fanc: QEfls rEos GRA ,DH/CAL SOLUT/ON VA NA D/UM PERMENDUR COEFF/UIEIVT DEMAGIVETlZAT/ON FORGE OERSTEDS /NVEN TOR.

"Al/en A. Chernosky,

BY @M ,amaw

AGENT VARIABLE GAP RELUCTANCE TRANSDUCER Allen A. Chernosky, Houston, Tex., assignor, by mesue assignments, to Jersey Production Research Company, Tulsa, Okla., a corporation of Delaware Application July 19, 1954, Serial No. 444,171

Claims. (Cl. 340-17) This invention relates to geophysi'cal prospecting. More particularly, this invention relates to a variable reluctance transducer for detecting air borne, water borne or solid borne waves and producing an electrical signal indicative of the character of the detected waves.

Transducers in general use are of three types:

(l) Displacement.

(2) Velocity.

(3) Acceleration.

All of the aforementioned types depend for their electrical signal on the relative movement of one element in the transducer, usually called an inertia mass, with respect to another element which moves in response to the impinging waves. Motion sensitive transducers are displacement, velocity or acceleration sensitive depending upon the frequencies applied and the natural frequency of the transducer. Displacement sensitivity occurs for a given transducer when the applied frequencies are much higher than the natural frequency of the transducer. Velocity sensitivity occurs when the applied frequency is equal to the natural frequency. Acceleration Vsensitivity occurs when the applied frequency is low relative to the natural frequency. More recently, a dilferent type of transducer has been utilized in certain geophysical prospecting. These transducers have been named squeeze or pressure transducers and generate an electrical signal as the result of a deformity of the transducer occasioned by the pressure of the impinging waves. An example of a pressure orV squeeze type transducer is the magnetostrictive seismometer. The magnetostrictive core of magnetostrictive seismometers is deformed when the sesmic waves impinge upon the magnetostrjictive element and a change in electric current occurs as a result of the deformity. The present invention, in several of its embodiments, makes use of the pressure or squeeze principle and in other of its embodiments makes use of the relative-movement principle for the detection of impinging waves and the generation of electrical signals ndicative of the character'of said waves.

My invention when employed as a variable reluctance type seismometer is used with the conventional amplifier and recorder for detecting and recording sesmic waves set up by explosives or other means. The conventional variable reluctance type seismometer makes use of a permanent magnet for producing a permanent magnetomotive force. These conventional seismometers, all of which, in the past, have been of any one of the three motion types aforementioned, produce a change in voltage in response to the relative movement of a casing in which the permanent magnet is enclosed with respect to an armature suspended in the casing by means of a spring, which armature constitutes the inertia mass of the seismometer. However, the usual permanent magnet, because of its hard magnetic material, is not sensitive enough to detect and sufficiently indicate the very minute vibrations of some of the sesmic waves which it is desired to detect. 1

My invention makes use of a seismometer made of a soft magnetic material. My new seismometer is much more sensitive than the conventional variable reluctance seismometers, is very simple in construction and can be used as a velocity, displacement or acceleration type seismometer or a squeeze or pressure type seismometer. Soft magnetic material has been utilized before in variable reluctance'type seismometers. However, all previous variable reluctance seismometers employing soft magnetic material have been of the velocity, displacement or acceleration type and have been utilized to modulate an external source' of carrier current, it being i believed by previous sesmic prospectors that the soft magnetic material could not be utilized as a generator of electrical energy in response to sesmic waves. The use of a variable reluctance transducer utilizing a soft mag-- netic material to modulate a carrier current is described in the patent to J. P. Minton, 2,371,973, issued on March 20, 1945. I have made the important discovery that a variable reluctance seismometer can be made, utilizing a soft magnetic material, which can be used as a very sensitive generator of electrical signals in response to detected sesmic waves and hence does not need any external carrier current orother external source of energy in order to be effective. In addition, the utilization of a soft magnetic material which is highly sensitive to" even the slightest pressure makes possible a variable reluctance transducer which depends upon a pressure or squeeze action as distinguished from a velocity, displacement or acceleration type action.

It is an object, therefore, of my invention to provide an instrument which is simple in structure and is highly sensitive to detected waves.

It is a further object of my invention to provide a variable reluctance type seismometer which is an independent generator of electrical signals in response to detectedV waves and needs no external source of electrical energy.

Briefiy described, my invention consists of a loop or circuit of soft magnetic material broken by one or more relatively short air gaps comprising a permanently magnetizable circuit. This air gap is of the order of a few .thousandths of an inch. Electromagnetically associated with the soft magnetic material is an electrical coil, the voltage of the coil being varied when the width of the air gap is altered in response to impinging sesmic waves thereby producing a varying electrical voltage.

Other objects and features of the invention will become more apparent upon a consideration of the accompanying drawings and following specification, wherein are disclosed several embodiments of the invention with the understanding that such changes may be made therein as fall within the scope of the appended claims without departing from the spirit of the invention.

In the drawings:

Fig. 1 shows a perspective view of mynew seismometer.

Fig. 2 is a perspective view of a second embodiment of my new invention.

Fig. 3 is a perspective view of another embodiment of my invention.

Fig. 4 is a perspective view of still another embodiment of my invention.

Fig. 5 is a front elevational view of another embodiment of my invention.

Fig. 6 is a perspective view of still another embodiment of my invention. I

Fig. 7 is a rear elevational view of the embodiment shown in.Fig. 6.

Fig. 8 isa perspective view of an embodiment of my i Patented Jan. 5, 1860 embodimentof, my inventiontused as a motion type.

sensitivity;v due to; increased permeability Vto alternatingI fluitl of.: at seismometer;utilizing soft-V magnetic. material having-approximately-.the; same ;residual .magnetism'v as the conventionaly seisrnometerswhich;v make use of ahard magnetic, material.

In. Fig-@11 thereis shown-.oneembodiment of my invention.. l .The seismmnetei.:h consistsf--of apair; of: semi-,- cylindrical mem-hers;z S-;Which ;are ;machined -from .fa frnag-l f netic, material; leaving ;the:cantilever .fextensionst-Q ;whichfunction as gseparator -springs When. ;spacers ltkare Mused at the irgextremitiesu; T hegspacerstlfl:preferably: arezrnadef. offnotrmagneticinaterial;v When the-twomembers are f connected` togetherV at.` the: extremitieswof: the:V cant-ilever.

extensions 9; by means of jscrews;v .asu'bstantially hollow cylindrical seismometen is producedwhich isV of :a very; convenientshape to 'bev placed ;about/a cable-such asthe cables used in marine prospecting; or-land prospecting.

Wound about the members8-are coils 12. Spacer-;10fis utilized .to provide atvery` minute;separation-;or-airsgapg 11 between theetwosemi-cylindrical rnembers 8.f;,V This.

spacermayf beof the :orderpf Wmoowof an inch. The;

cantilever -extensions 9'- have,.a naturalmechanical fre-fV quency of from-:300-to 2000 cycles per second. A' high natural mechanical ;frequency for ,extensions f9-servesas ;a means tol diminishltheoutplutv at the unwanted low frequencies, such as extraneous-ground noises,,etc; V This 2,920,307 i f o high natural. mechanical frequency also preventsv the I settinglupv ofaresonance in the seismometerl caused by the impingement of seismic frequencies Which; are close to the natural frequency of the. extensions-snce. seismic' frequencies are'lower than theyinstrumentis-meehanical 'frequency, However; becausel of-'ther. reduced;I mechanical gain of. the extensions 9, itis-highlyfdesirable that a very sensitive generator of electrical signal power be utilized, Therefore,.- the use of afhardmagnetie materialin'the making of the semi-cylindrical members ,S-v would. result* in an ineflicient instrumentbecausea: hard magnet-fematerial has a low permeability .and it isznot sensitive enough; to air-.gap variation.

high sensitivity to*` air-.gap,variation.-fi The .init-ial' mag:

netization of thedevicepshown-in Fig. 1,.,as,-wel1-as;the..

other devices described; may be accomplished byjapplying a high amplitude momentary direct current through the signal 'coil.v When .the members fS are made of a soft magnetic material, and the air gap 11 is made-of the order of a few.thousandths of an. inch, my new seismometer serves very efiectively as a generator of electrical signals in response to the pressure of detected seismic waves. This new instrument is an independentgenerator of a voltage and does not need Vthe use of an external source of .electricity such as acarn'er signaL- Hence the record- IhFi'g'r 3 'there is shown anoth'er'embodiment ;of-my invention which also can begusedp as ascnreezeiior` In the .present-desigmga `lsoft -.rnag-; netc material whichh has auhigh;permeabilityfis-utilized. as a relatively. permanent magnetomotive force: with.very;

: Ylength can be represented bythe intersections of the corresponding lpermeance coeffifcient values and .the demagpressurf'ftype seisrrrometer.`` This embodiment -isffadg vantageous in winding'separtate coils=122 Tofthis end-'themembers :Btaref'shaped- :so .that :when :connected-@together 4.. two hollow volumes 19 are formed which are connected by a very narrow slit or air gap 20.

In Fig. 4 there is shown an embodiment of my invention which is similar to that of Fig. 2 but has attached thereto a strip of hard magnet 22. This embodiment may be used at a sacrifice of sensitivity with a slight gain in permanency of magnetization;

The'embodiment shown" in Fig.y 5" has as. separator springs slightly oversize tubing 23 accommodated in slots 24; VThis embodiment hasfithe; advantage off giving an even springing effect over. any desired length".` of members 8.

In theembodiment sh'ownin Figs; 'and 7, the lsemicylindrical members 8 each hasvonlyone pair of stiff.

springs 9 at one of its longitudinal extremities. The pair of stiff springs 9 'of each member 8 is connected to the other member 8 'by screws 26 screwed through blocks 25. Recesses 28`areprovided in'each semi-cylindrical member 8 .to accommodate screws 26.

ups. In Fig. 8 the pair of soft magnetic material members are machined in H-shape and have thel usual-stiff cantilever springs 9 separatedr by spacer 10. The coil lis wrapped about the H member 16 in a longitudinal groove 17 within said `member 16.H The-lower member 16has attached,theretoatplurality of-'prongs 18.which are vset into the ground in `land prospecting. As canbe seen, the

lower member 16 moves in response'to any impinging seismic waves and the motion of the lower member with respect to the upper member 16 sets tup. an alternatingcurrent intthe coils-121 In Fig, 9ftheupperand lower members are made-with' a projectingcore 21 and thetcoils 12-are lwrapped about the vprojecting core.` The usualextension 9 and spacer 10 are alsoV provided.

The. embodiment shown in Figs. .10 and ll which is particularly adapted for prospecting in marshland is provided.

with an. armature. VThe armature.30 isprovidednwith Va .plurality of: recesses. 31 separatedby approximately A plurality of Vstiff springs 32is:utilized.to suspend.. the armature- 30 Within'the housing.. The soft .magneticV material consistsof 'a magnetic housing 33 and core 34t..

A coil 12 is wound.about.core- 34.

Some illustrative. examples -will be. worked ;using Vthe demagnetization curve of Vanadium` Per/mendur,` asoft magnetic material. having a coercive force of '2.7 oersteds, and'thedemagnetization curve of Hyflux Alnico, a hard magnetic material havingua. coercive force of about-600.' oerstteds; v f

Selected air gap spacesv correspondingto a given magnet netization curveof'the materialto bjeused; The vpermeance coetlicient can be taken as equaltotheratio of the magnet length to the air .gapflength`, which is also equal. to the slope of a vector through theorigin. TheV vectors representingseveral `values ofthe permeancecoefficient .are shown on' each of the. .curyes onFigs. 12,'and 13.' The local magnetization-demagnetization loops such as aa'A and tbbffforsmall air gap variationsjcan be. representedby operating *lineshaving' a slope equal to' the reversible` 'permeability. 1 VThe operating line ;isV drawn through;Atheintersection ofthe lower permeance coei-- cie'nt since2'flux restoration along minorloops is not `Vcornplete." lIncre'mentalchanges infi fiX density lcor-responding v to 'Iiiicrem'ental gap changes-'can kbe taken? from the Vintersectioniof-fthelv permeance' coefl'icient lvectors and on the operating line.

The outward ends of springs 9, in this embodiment; are flush-iwith the extremity of the member S-to whichV it isscrewed; The springs9 are thereby protected against-y damage caused by hard' Approximate sensitivities in kilogauss per inch for various permeance coeflicients and gap spaces will be determined.

y=operating line P=permeance coeficient Lm gauss --L--slope of permeance coefficient vector-- oersteds Il=flux density in gauss Lm=total magnet length Lg=total air gap length change in flux density change in air gap V.R. sensitivity from curve= S= -=25.7 K. gauss/in.

:25. K.G./in.

`It can be seen from an examination of these results that a range of sensitivities can be obtained from a magnet of soft or hard material. Where practical dimensions are used such as from .002-.004 air gap, it can be seen that the Vanadium Permendure sensitivity is far greater. In all cases if the permeance coefiicient is an optimum, the highest sensitivity comes from using the shortest magnet. If a very short Alnico magnet circuit is utilized a higher sensitivity results, but for many uses the size is too small for winding an appreciable amount of wire. Magnetic material having a reversible permeability of or more is suitable for use in my new generator. Of course, the higher the reversible permeability the more sensitive the instrument will be.

If desired, the soft magnetic material of all the embodiments of my invention may be made of laminated consu'uction.

From the foregoing description and analysis, the superiority of my invention over previous variable reluctance type transducers is clearly illustrated.

Having described my invention, I claim:

1. A generator device for detecting seismic waves and producing electrical signals indicative of said seismic waves, comprising: a magnetic circuit consisting of a pair of semi-cylindrical members of soft magnetic material having high residual magnetism, and at least two air gaps of the order of a few thousandths of an inch; each of said semi-cylindrical members having a pair of stiff spring extensions integrally connected to the ends thereof; said members being connected together at the extensions thereof and separated by spacer means to form an approximately hollow cylinder; said spacer means 6 being adapted to provide said air gaps between said semi-cylindrical members; a coil wound about at least one of said semi-cylindrcal members, a substantial voltage being inducible in said coil by minute changes in said small air gaps.

2. A generator device for detecting seismic waves and producing electrical signals indicative of said seismic Waves, comprising: a magnetic circuit consisting of a pair of semi-cylindrical members of soft magnetic material having high residual magnetism, and at least one air gap of the order of a few thousandths of an inch; at least one spring extension connected to each member, each spring extension having a high'natural frequency; spacer means spacing apart said spring extensions adapted to provide said at least one air gap; and a coil wound about at least one of said members, said soft magnetic members being deformed by the pressure of impinging seisrnic waves to produce a voltage across said coil.

3. A generator device for detecting'sesmic waves and producing electrical signals indicative of said seismic waves, comprising: a magnetic circuit consisting of a pair of members of soft magnetic material having high residual magnetism, and at least one air gap of the order of a few thousandths of an inch, at least one spring extension connected to each member; spacer means positioned between said spring extensions to provide said at least one air gap; and a coil wound about at least one of said members.

4. A generator device for detecting seismic waves and producing electrical signals indicative of said seismic waves, comprising: a magnetic circuit consisting of a pair of H-shaped members of soft magnetic material' with high residual magnetism, and at least two air gaps each of the order of a few thousandths of an inch; each of said H-shaped members having a pair of stiff spring extensions integrally connected to the ends thereof; said members being connected together at the extensions thereof and separated by a spacer to provide said air gaps; one of said H-shaped members being adapted to move 'with the motions of the earth; a coil wound about at least one of said H-shaped members, a substantial voltage being inducible in said coil by a change in said air gap caused by said seismic waves.

5. A generator device for detecting seismic waves and producing electrical signals indicative of said seismic waves, comprising: a 'magnetic circuit consisting of a pair of semi-cylindrical members of soft magnetic material having high residual magnetism, and at least two air gaps each of the order of a few thousandths of an inch; tubing spring means separating said members to provide said air gap; and a coil wound about at least one of said semi-cylindrical members, a substantial voltage being inducible in said coil by minute changes in said air gaps.

References Cited in the file of this patent UNITED STATES PATENTS 252,256 Rogers Jan. 10, 1882 1,640,538 Du Bois-Raymond Aug. 30, 1927 1,748,993 Purdy Mar. 4, 1930 1,889,398 Bishop Nov. 29, 1932 2,269,453 Gayhart Jan. 13, 1942 2,311,079 i Parr Feb. 16, 1943 2,328,222 McCarty Aug. 31, 1943 2,348,225 Petty May 19, 1944 2,637,823 Anderson et al. May 5, 1953 2,708,742 Harris May 17, 1955 OTHER REFERENCES Electrical Engineers' Handbook, Foster, 6th ed., 1910, page 345. 

